The present invention is directed to rechargeable batteries, such as lithium-ion or lithium-polymer rechargeable battery cells and other rechargeable battery chemistries, and in particular to overcharge protection circuits and devices therefor.
Lithium based rechargeable battery cells are subject to potentially unsafe failure modes if severely overcharged. Numerous methods of prior art overcharge protection have been proposed and implemented in lithium cell products and battery pack products to avoid the potential serious consequences of overcharge conditions. Few of these methods provide fully adequate protection at a very low cost. Many of these methods are not fail-safe in nature. Moreover, few known methods of overcharge protection have been proposed that can be included in the battery cell structure.
U.S. Pat. No. 5,608,307 to Garrett et al. discloses a shunt regulator control method for batter packs. However, this prior art control method is primarily responsive to excess charging current, which may not adequately protect a lithium battery cell. In addition, this prior method does not address protection for the shunt regulator device from thermal run-away due to high power dissipation, particularly under overload charging conditions that might occur from a run-away defective battery charger. Moreover, the prior method does not include provisions to be fully fail-safe.
It is desirable to provide a protection device for use with lithium battery cells and other battery cell chemistry applications to protect the battery cells from overcharge conditions, and including optional additional features to achieve fail-safe protection by protecting the circuit elements themselves that protect the battery cells.